The present invention relates to a storage/transport container for radioactive material such as spent nuclear fuel rods. More particularly this invention concerns a method of making such a container.
A standard container for nuclear waste products comprises an inner shell having a cylindrical side wall and planar floor, a similarly shaped outer shell spacedly surrounding the inner shell, a mass of concrete or the like in the space between the shells, and a cover. The material being stored or transported is loaded into the inner shell and the cover is installed. is The steel walls of the shells and the concrete between them provides shielding.
Heat evolves from the waste so that it is standard as described in German patent document 2,817,193 filed Apr. 20, 1978 by R. Christ to provide webs or struts of heat-conductive material between the inner and outer shells. Thus heat is conducted to the outer shell where it can dissipate to the atmosphere without overly heating the inner shell or the contents of the container.
Such containers are mass produced and, once filled, are normally not reused so that they must be made at the lowest possible cost. The main bottleneck in production is the laborious installation of the heat-dissipating webs between the shells.
It is therefore an object of the present invention to provide an improved method of making a storage/transport container for radioactive material.
A storage/transport container for radioactive material has according to the invention has a metallic outer shell, a metallic inner shell concentrically received in the outer cell and defining therewith an annular space, and an annular and continuous heat-conductive meander strip in the space. The strip is formed unitarily with a plurality of angularly spaced inner segments engaging the inner shell, respective angularly spaced outer segments engaging the outer shell, and respective generally radially extending webs extending between the inner and outer segments.
The meander strip, which is of constant width and thickness, can easily be formed into the desired shape at very low cost by a simple roll-stamping procedure. When fitted in the space between the inner and outer shells it forms an excellent heat-conducting bridge. There is no need to position individual elements in place and then individually secure them.
The inner segments according to the invention each have angularly spaced opposite ends from which the webs extend and which abut the ends of adjacent flanking inner segments. Thus the inner-segment ends can be joined together to form an inner ring tightly surrounding the inner shell which may be annularly continuous or split.
The container in accordance with the invention comprises a plurality of such strips axially offset from each other with the inside and outside segments of adjacent strips staggered angularly. Thus the concrete filling will extend continuously over the entire space between the shells, joined together axially of the container into a single mass in which the strip webs are imbedded.
The inner segments have a curvature corresponding to a curvature of an outer surface of the inner shell and the outer segments have a curvature corresponding to a curvature of an inner surface of the outer shell. This ensures excellent contact and good heat transfer from the inner shell to the outer shell. The webs are under prestress and press the segments against the respective shells to further augment the heat-conducting contact.
The inner and outer shells according to the invention have respective base plates spaced axially from each other. An array of metallic heat-conducting strips between the base plates have inner ends engaging the inner-shell base plate and outer ends engaging the outer shell. Thus even the floor of the inner shell is set up to conduct heat away from the charge in the container to the outer shell.
The storage/transport container according to the invention is made by first fitting around a metallic inner shell an annular and continuous heat-conductive meander strip having a plurality of angularly spaced inner segments engaging the inner shell, respective angularly spaced outer segments, and respective generally radially extending webs extending between the inner and outer segments. This meander strip may be fixed to the inner shell. Then the meander strip is radially inwardly compressed and the other shell is fitted over the inner shell and meander strip. Then the compression of the meander strip is released so that the outer segments bear on the outer shell. Finally a space between the inner and outer shells is filled with concrete. The radial compression of the radially elastically deforms the webs that stay radially slightly deformed in the finished container so that good contact with the outer shell is ensured.